The present invention relates generally to the construction of flexible, torque-transmitting devices, and more particularly to the construction of drive cables for rotation of ultrasonic transducers for use in vascular catheters.
Intravascular imaging of blood vessel lesions prior to percutaneous transluminal angioplasty, atherectomy, and other interventional procedures, promises to be of great benefit. A particularly successful design for an intravascular imaging catheter employs a rotatable ultrasonic transducer, where the transducer is attached to the distal end of a flexible drive cable. The transducer may be rotated within a catheter body or sheath in order to transmit an ultrasonic signal and produce a video image by well-known techniques.
Although very successful, the need to reduce the size of the drive cable to very small diameters (to be compatible with introduction into very small coronary arteries) presents a number of technical challenges. In addition to the very small diameter, the drive cable should be highly flexible so that it can pass through the tortuous regions of the vasculature, particularly the coronary arteries. It is also very important that the drive cable provides uniform rotation along its entire length, i.e., avoid rotational wind-up which can cause variations in the rotational speed of the transducer and result in image distortions.
The construction of transducer drive cables for intravascular ultrasound devices is further complicated by the desire to run transducer lead wires or transmission lines through a lumen in the cable itself. Such designs attempt to avoid an increase in an effective diameter which may result from placing the leads on the surface of the drive cable. Coaxial lead cables have been utilized in the past and have the added advantage that they provide radio frequency (RF) noise shielding. Coaxial cables, however, suffer in that they are generally large and difficult to use in the smallest intravascular devices, e.g., coronary devices. Coaxial cables also are typically manufactured separately from the drive cables, which requires that the drive cable lumen be large enough to allow the coaxial cable to be fed through. The resulting gap between the coaxial cable and drive cable further adds to the drive cable""s overall outer diameter.
It would be therefore desirable to provide improved drive cables for ultrasonic transducers and other rotatable electrical sensors. It would be particularly desirable to provide drive cables which can be constructed to have small diameters while still incorporating transmission lines. Preferably, the combined drive cable and transmission line will provide uniform torque-transmission along the entire length of the drive cable in order to produce ultrasonic images having a minimum distortion. The drive cables should further provide sufficient RF shielding of the electrical transmission lines.
The present invention provides for integrated flexible drive cables and coaxial transmission lines for use in catheter systems. In one embodiment, the invention provides a catheter system comprising a catheter body having a distal end, a proximal end and a working lumen. A drive cable extends through the working lumen and comprises an outerwound layer, an innerwound layer and a central lumen. A coaxial cable is provided comprising a conducting core and an insulation layer. The coaxial cable is disposed to extend through and fill the central lumen.
In one aspect of the invention, the innerwound layer comprises a combination of stainless steel wire and at least one material comprising copper, gold, silver, aluminum, magnesium or an alloy made from at least one of these metals. In this manner, the innerwound layer provides exemplary mechanical properties from the stainless steel, and also exemplary shielding properties from the other metal or metal alloy.
In another aspect, the drive cable has an outer diameter between about 0.005 inches and about 0.150 inches. Such a diameter facilitates the use of the drive cable with small catheter bodies. In one aspect, both the innerwound layer and outerwound layer comprise stainless steel wire. In this manner, the drive cable comprises two layers of stainless steel wire.
In another aspect, the innerwound layer comprises a shape memory or superelastic alloy metal wire, such as wire made from nitinol (nickel titanium), nickel titanium copper, nickel titanium aluminum, or the like. In one aspect, the outerwound layer comprises a shape memory or superelastic alloy metal wire.
In one particular aspect, the catheter system further comprises a working element operably attached to the drive cable. In one aspect, the working element is a transducer. Alternatively, the working element is an annular array of transducer elements.
In another particular aspect, the coaxial cable further comprises a shield layer. Such a shield layer facilitates the conduction of electrical signals through the conducting core without experiencing external electrical interference which may adversely affect the signals. In one aspect, the shield layer comprises at least one material selected from a group of materials consisting of silver-plated copper, gold, aluminum, and alloys made from at least one of these metals. Such a selection of metals facilitates the shielding capability of the shield layer.
In another aspect, the drive cable, which includes a coaxial cable containing a shield layer disposed within the drive cable""s central lumen, has an outer diameter between about 0.005 inches and about 0.150 inches.
In one preferred embodiment, the invention provides an integrated drive cable and transmission line for a catheter comprising a conducting core having a layer of insulation. The integrated drive cable and transmission line further includes an innerwound layer adjacent to and surrounding the layer of insulation, and an outerwound layer adjacent to and surrounding the innerwound layer.
In one aspect, the innerwound layer comprises a combination of stainless steel wire and at least one material selected from a group of materials consisting of copper, gold, silver, aluminum, magnesium, copper alloy, gold alloy, silver alloy, aluminum alloy and magnesium alloy. Such an innerwound composition facilitates the shielding of external electrical interference as well as providing a drive cable of sufficient flexibility and strength. In another aspect, the outerwound layer has an outer diameter between about 0.005 inches and about 0.150 inches.
In one particular aspect, the innerwound layer comprises stainless steel wire to assist in providing uniform rotation over the length of the cable. In another aspect, the outerwound layer also comprises stainless steel wire.
In still another preferred embodiment, the invention provides an integrated drive cable and transmission line for a catheter comprising a conducting core having a layer of insulation, and a shield layer adjacent to and surrounding the layer of insulation. The drive cable and transmission line further comprises an innerwound layer adjacent to and surrounding the shield layer. An outerwound layer is provided adjacent to and surrounding the innerwound layer.
In one aspect, the shield layer comprises at least one of silver-plated copper, gold, aluminum, silver-plated copper alloy, gold alloy and aluminum alloy. In another aspect, the outerwound layer has an outer diameter between about 0.005 inches and about 0.150 inches. In a further aspect, the innerwound and outerwound layers comprise stainless steel wire.
In one aspect, the innerwound layer comprises a shape memory or superelastic alloy metal wire, such as wire made from nitinol (nickel titanium), nickel titanium copper, nickel titanium aluminum, or the like. In another aspect, the outerwound layer comprises wire made from a shape memory or superelastic alloy metal.